Image uploader only works in IE

Hi

I just updated two blogs from 2.5 to 2.7 and both are seeing the same problem with the image uploader. Using Firefox (3.0.5/XP) when I click the insert image button the uploader appears full screen rather than in an IFrame. The uploader seems to basically work, but when I get to the end and hit the Insert button to return to the post I get a blank white screen.

All of this functionality works fine when using IE7, and I’ve tried disabling all of my FF plugins. I’ve seen reports of similar problems around the place but no solutions (and yes, I’ve read the sticky at the top of the forum and tried everything it suggests).

Is this a known issue with FF3? Are there any other things I can try (or tests I can run to help diagnose)?

Any help much appreciated!